1. Field of the Invention
The present invention relates to a method of connecting optical fibers.
2. Description of the Related Art
A holey fiber is an optical fiber having air holes arranged in a periodic manner in a cladding region. The cladding region surrounds a core region. The cladding region has reduced average refractive index because of the presence of the air holes so that a light passes almost entirely through the core region because of the total reflection of the light.
Because the refractive index of holey fibers can be controlled by controlling various parameters of the air holes, the holey fibers can realize unique properties that can not be realized in the other optical fibers such as endlessly single mode (ESM) and anomalous dispersion at a short wavelength. The ESM means that a cut-off wavelength is not present and a light is transmitted in a single mode at all wavelengths. With the ESM, it is possible to realize an optical transmission at a high transmission speed over a broadband.
A holey fiber is sometimes connected to another optical fiber, which can be a holey fiber or an ordinary optical fiber, to make a longer optical fiber. However, when the holey fiber is fusion spliced to another optical fiber, the air holes in an arc-discharged and heated joint section and in a vicinity of the joint section collapse. If the air holes collapse, it is difficult to confine light in the core region, so that confinement loss increases.
A conventional technology for reducing confinement loss is disclosed in Japanese Patent Application Laid-open No. 2004-177804. Specifically, duration or intensity of the arc discharge is adjusted to prevent the collapses of the air holes. Furthermore, Japanese Patent Application Laid-open No. 2007-72418 discloses another conventional technology in which fusion spliced portions are etched using etching solutions to attain a thin fiber after fusion splicing a double clad holey fiber and a multimode optical fiber without air holes. Hydrofluoric acid can be used as the etching solution.
However, with the former conventional technology, the arc discharge duration or intensity are restricted, so that the desirable mechanical strength of the spliced portions can not be maintained. With the latter conventional technology, originally thin optical fibers are made to be thinner, so that strict controls of etching amounts are required. Single-mode holey fibers are inherently ultrathin, so that the etching is difficult to be applied to the single-mode holey fibers. Furthermore, the etching may cause surface exposures of the air holes which may increase confinement loss due to entries of particles or foreign objects into the exposed air holes.